/Engine/Plugins/FX/Niagara/Source/Niagara/Public/NiagaraSystemInstance.h
Final phase of system instance tick. Must be executed on the game thread. Returns whether the Finalize was actually done. It's possible for the finalize in a task to have already been done earlier on the GT by a WaitForAsyncAndFinalize call.
void FinalizeTick_GameThread ( bool bEnqueueGPUTickIfNeeded )